Various types of medical equipment have been utilized to deliver controlled volumes of liquid and gaseous substances to patients. One field that involves the administration of such fluids is radiology, wherein a small amount of carbon dioxide gas or an alternative contrast media is delivered to the vascular system of the patient in order to displace the patient's blood and obtain improved images of the vascular system. Traditionally, this has required that the CO2 or other media first be delivered from a pressurized cylinder to a syringe. The filled syringe is then disconnected from the cylinder and reconnected to a catheter attached to the patient. If additional CO2 is needed, the syringe must be disconnected from the catheter and reattached to the cylinder for refilling. Not only is this procedure tedious and time consuming, it presents a serious risk of introducing air into the CO2 or contrast fluid at each point of disconnection. Injecting such air into the patient's blood vessels can be extremely dangerous and even fatal.
Recinella et al., U.S. Pat. No. 6,315,762 discloses a closed delivery system wherein a bag containing up to 2,000 ml of carbon dioxide or other contrast media is selectively interconnected by a stopcock to either the chamber of a syringe or a catheter attached to the patient. Although this system does reduce the introduction of air into the administered fluid caused by disconnecting and reconnecting the individual components, it still exhibits a number of shortcomings. For one thing, potentially dangerous volumes of air are apt to be trapped within the bag. This usually requires the bag to be manipulated and flushed multiple times before it is attached to the stopcock and ultimately to the catheter. Moreover, this delivery system does not feature an optimally safe and reliable, foolproof operation. If the stopcock valve is incorrectly operated to inadvertently connect the carbon dioxide filled bag or other source of carbon dioxide directly to the patient catheter, a dangerous and potentially lethal volume of CO2 may be delivered suddenly to the patient's vascular system. It is medically critical to avoid such CO2 flooding of the blood vessels.